Wireless communications systems continue to grow in popularity and utilization. One such example is cellular networks, which continue to grow worldwide and add ever expanding coverage areas and enhanced cellular communications formats to increase bandwidth and data communication rates.
Another important area of wireless communications is governmental communications systems, which are particularly important for disaster and emergency response operations. Typically, trunked radio systems are used for such applications, as they allow for a given number of channels (i.e., communications frequencies) to be used to establish numerous talk groups. A control channel sends packets of data to enable talk group members to communicate with one another, regardless of frequency. This advantageously allows many people to conduct conversations over a relatively small number of frequencies. By way of example, trunking systems are used to provide two-way communication for fire departments, police and other municipal services, who all share spectrum allocated to a city, county, or other entity.
One such example of a trunked radio frequency (RF) communication system is described in U.S. Pat. No. 5,553,243 to Harrison et al. This patent describes an approach for determining the fidelity of communications over a communications channel. Portable/mobile radios freely roaming between multiple trunked RF communications sites calculate the fidelity of communications received over current and alternate channels with comprehensive, high bit error resolution using a weighted average error dispersion procedure. The weighted average error dispersion analysis generates, for each group of redundant messages (and in some instances sub-preamble bits) received by a roaming radio in each message frame, a weighted average error dispersion number whose incrementally increasing magnitude reflects deteriorating signal fidelity. Decisions about switching to alternate communications channels are made by the roaming radio based on the incrementally changing weighted error dispersion number.
A relatively new approach to trunked radio for governmental use is being developed as Project 25 (P25), or APCO-25, which encompasses a suite of standards for digital radio communications for use by federal, state/province and local public safety agencies in North America to enable them to communicate with other agencies and mutual aid response teams in emergencies. P25 takes advantage of the technological advances and expanded capabilities of digital radio.
Despite the existence of systems such as P25, further enhancements for wireless communications systems may be desirable in some applications.